validtyped

A runtime and compile-time type checker library.

Simple Example

import * as v from 'validtyped';
 
const data: any = /*... some data of unknown type */ {};
 
const mySchema = v.object({
    a: v.string(['one', 'two', 'three']),
    b: v.number(),
    c: v.object({
        d: v.array(v.number())
    }),
});
 
if (mySchema.isValid(data)) {
    // these are typesafe operations
    data.a.match(/.*/);
    data.c.d.map(x => x * 2);
 
    // this is not valid at compile-time
    data.e + 1;
}
 

Why?

At the boundaries of any typescript application, assumptions have to be made about what the expected types are. In any scenario when making api calls, an application must either trust that the correct data will be returned or must validate the data given to it.

To maintain these assumptions with TS would require code like:

const schema = {
    type: 'object',
    properties: {
        a: { type: 'string' },
        b: { type: 'number' },
    }
}
 
interface Thing {
    a: string;
    b: number;
}

While this is totally reasonable code, it requires specifying the shape of every object twice.

Because JSON Schema is such a commonly used standard, many amazing JSON Schema validators exist on npm. Instead of building yet another validator to compete with these, validtyped makes use of ajv for the underlying validation logic. As such, this project is simply a thin wrapper over ajv to bring compile-time typescript types, and run-time JSON Schema types together:

import * as v from 'validtyped';
 
const schema = v.object({
    a: v.string(),
    b: v.number(),
});
 
type Thing = v.ValidType<typeof schema>;

Api Docs

any

Creates a validator instance that is always true. This is useful for specifying that an object must have a given parameter, but you don't care what type that parameter is.

Example:

import * as v from 'validtyped';
 
const data: any = getData();
 
const validator = v.object({ a: v.string(), b: v.any() });
 
if (validator.isValid(data)) doThing(data); // typeof data => `{ a: string, b: any }`
else throw new Error('oops!'); // typeof data => `any`

array

Creates a Validator instance that matches on arrays of the given type.

Param	Description
v	A Validator instance that specifies the shape of the array elements.

Example:

import * as v from 'validtyped';
 
const validator = v.array( v.number() );
const data: any = getData();
 
if (validator.isValid(data)) doThing(data); // typeof data = `number[]`;
else throw new Error('oops!'); // typeof data = `any`

boolean

Creates a validator instance that is true when the given type is a boolean.

Example:

import * as v from 'validtyped';
 
const validator = v.boolean();
const data: any = getData();
 
if (validator.isValid(data)) doThing(data); // typeof data => `boolean`
else throw new Error('oops!'); // typeof data => `any`

intersect

Creates a Validator instance that matches on both of the given possible types.

Param	Description
v1	A Validator instance that the specified type must match.
v2	A Validator instance that the specified type must match.

Example:

import * as v from 'validtyped';
 
const validator = v.intersect( v.object({ a: v.string() }), v.object({ b: v.number() }) );
const data: any = getData();
 
if (validator.isValid(data)) doThing(data); // typeof data = `{ a: string, b: number }`
else throw new Error('oops!'); // typeof data = `any`

nil

Creates a validator instance that is true when given null.

Example:

import * as v from 'validtyped';
 
const data : any = getData();
 
const validator = v.nil();
 
if (validator.isValid(data)) doThing(data); // typeof data => `null`
else throw new Error('oops!'); // typeof data => `any`

nominal

Creates a validator instance that passes type checking through to the given validator. Operates as an identity function for the runtime Validator type, but annotates the compile-time encapsulated Validator<T> with a nominal string.

This is useful for marking ids or other fields as being a specific type that should not be edited.

Param	Description
v	The validator instance that will be passed through for checking runtime correctness.
s	The nominal type tag for compile-time types.

Example:

import * as v from 'validtyped';
 
const validator = v.nominal(v.string(), 'id');
const data: any = getData();
 
if (validator.isValid(data)) doThing(data); // typeof data => `Nominal<string, 'id'>`
else throw new Error('oops!'); // typeof data => `any`
 
const id = 'user-id' as Nominal<string, 'id'>;
const newId = id + '-new'; // typeof data => `string`. Since we've modified this type, it can no longer be an `id`.

number

Creates a validator instance that is true when the given type is a number.

Example:

import * as v from 'validtyped';
 
const validator = v.number();
const data: any = getData();
 
if (validator.isValid(data)) doThing(data); // typeof data => `number`
else throw new Error('oops!'); // typeof data => `any`

object

Creates a validator instance that validates the given data is an object, and every property of that object matches the given schemas. By default, all listed properties are required. By default, unlisted properties are also allowed.

Param	Description
o	An object whose keys will be required keys of the valid type and whose properties are Validator instances matching the valid property's types.
opts	[optional] An options object
opts.optional	[optional] A list of keys that should be marked as optional in the valid type.

Example:

import * as v from 'validtyped';
 
const validator = v.object({ a: v.string(), b: v.number() });
const data: any = getData();
 
if (validator.isValid(data)) doThing(data); // typeof data = `{ a: string, b: number }`;
else throw new Error('oops!'); // typeof data = `any`

partial

Creates a Validator instance that matches on objects with no required keys, but mandated types for certain keys if they do exist.

Param	Description
v	A Validator instance that specifies an object type.

Example:

import * as v from 'validtyped';
 
const validator = v.partial( v.object({
 a: v.string(),
 b: v.number(),
}));
const data: any = getData();
 
if (validator.isValid(data)) doThing(data); // typeof data = `{ a?: string, b?: number }`;
else throw new Error('oops!'); // typeof data = `any`

record

Creates a Validator instance that matches on objects with any keys, and whose properties match the given Validator.

This is useful for "dictionary"-like objects, for instance a record of users by userId.

Param	Description
types	A Validator instance that specifies the right-side types of the record.

Example:

import * as v from 'validtyped';
 
const validator = v.record( v.number() );
const data: any = getData();
 
if (validator.isValid(data)) doThing(data); // typeof data = `Record<string, number>`;
else throw new Error('oops!'); // typeof data = `any`

string

Creates a validator instance that is true when the given type is a string.

Param	Description
union	[optional] an array of possible string literals that the valid data could take.

Example:

import * as v from 'validtyped';
 
const validator = v.string();
const data: any = getData();
 
if (validator.isValid(data)) doThing(data); // typeof data => `string`
else throw new Error('oops!'); // typeof data => `any`

union

Creates a Validator instance that matches on any one of the given list of possible types.

Param	Description
v	A list of Validator instances that specify the possible types that the valid type could take.

Example:

import * as v from 'validtyped';
 
const validator = v.union([ v.string(), v.number() ]);
const data: any = getData();
 
if (validator.isValid(data)) doThing(data); // typeof data = `number | string`
else throw new Error('oops!'); // typeof data = `any`

Validator

A Validator<T> instance is an encapsulated pair of some TS type T and a corresponding JSON schema.

A Validator already knows how to map from T to its json schema: using a json schema validator. Additionally, a Validator can perform simple algebraic operations with other Validators resulting in more complex validatable types.

A Validator will always maintain a valid json schema representation of the type, T, that it encapsulates. The underlying json schema can always be accessed with getSchema().

Example:

const stringValidator = new Validator<string>({ type: 'string' });
const numberValidator = new Validator<number>({ type: 'number' });
const strOrNum = new Validator<string | number>({ oneOf: [ { type: 'string' }, { type: 'number' } ]});
const strOrNum2 = stringValidator.or(numberValidator);

Validator.and

Creates a new validator that is true whenever the data matches this and v.

Param	Description
other	Another validator instance whose type will form an intersection with this encapsulated type.

Example:

import * as v from 'validtyped';
 
const v1 = v.object({ a: v.string() });
const v2 = v.object({ b: v.number() });
const v3 = v.object({ c: v.boolean() });
 
const and = v1.and(v2).and(v3); // { a: string, b: number, c: boolean }

Validator.getSchema

Returns the underlying JSON schema.

Example:

import * as v from 'validtyped';
 
const schema = v.string().getSchema();
console.log(schema); // { type: 'string' }

Validator.isValid

Predicate returning true if the given data matches the JSON schema. Acts as a type guard for the encapsulated typescript type.

Param	Description
thing	Any data of unknown type which will be validated.

Example:

import * as v from 'validtyped';
 
const userIdModel = v.nominal(v.string(), 'userId');
const userModel = v.object({ name: v.string(), id: userIdModel });
 
const x: any = getUserData();
if (userModel.isValid(x)) doThing(x);

Validator.or

Creates a new validator that is true whenever the data matches this or v.

Param	Description
other	Another validator instance whose type will form a union with this encapsulated type.

Example:

import * as v from 'validtyped';
 
const or = v.string().or(v.number()).or(v.boolean()); // string | number | boolean

Validator.orNull

Shortcut for .or(v.nil()) creating a nullable version of this schema.

Example:

import * as v from 'validtyped';
 
const nullableString = v.string().orNull();

Validator.setSchemaMetaData

Add meta-data to the underlying JSON schema. This is entirely un-observable information to the validator, but supplies the getSchema method to have a complete JSON schema with meta-data annotations.

Param	Description
meta	JSON schema meta-data (name, description, etc.)

Example:

import * as v from 'validtyped';
 
const validator = v.string();
validator.setSchemaMetaData({ name: 'string validator' });

Validator.validate

Takes data of unknown type and returns a discriminated union with either the data as the valid type, or an error object describing what part of the data did not match.

Param	Description
data	Any data of unknown type which will be validated.

Example:

import * as v from 'validtyped';
 
const stringModel = v.string();
 
const result = stringModel.validate(22);
if (result.valid) doThing(result.data);
else logger.error(...result.errors);

Validator.withOptions

Add additional validations to the generated schema. While most of these validations are not representable at compile time with typescript (minLength of a string for instance), it can be helpful to have the additional validations when validating runtime types.

Param	Description
opts	JSON schema specific options (for instance: { maxLength: 2, minLength: 0 })

Example:

const validator = v.string().withOptions({ minLength: 1 });
validator.isValid(''); // false
validator.isValid('hi'); // true

ValidType

Returns the encapsulated type of a Validator type.

Example:

import * as v from 'validtyped';
 
const validator = v.string();
 
type x = v.ValidType<typeof validator>; // `string`